I've been slowly finding my feet with my CNC router, and recently tried cutting the raptor model posted on the excellent Dinosaur skeleton dfx files (Dinosaur skeleton, and other models, DXF files.) thread.
The results were pretty good, but I'd like to get advice from those with a bit more experience.
I struggle to get material to stay completely flat to my table surface. It's always firmly clamped at the ends, but if I'm using a large sheet (and filling it with pieces to cut) it's not possible to get clamps around the whole perimeter, or bolts through the middle. At the moment, I stay with the machine during a job and press the sheet to the table near where it's cutting.
This leads on to the fact that, when cutting small pieces such as the dino files, you need some way of stopping them moving as they're cut out. At the moment, I'm using SheetCam's tabs facility, which works pretty well, but this then leaves quite a bit of work cutting the tabs with a knife and cleaning up the parts.
I was considering changing from a single 1/4" deep pass to one most of the way through, then a final shallow cut - this way I'd reduce the force of the cutter on the parts and may be able to get away with smaller, thinner, tabs.
The problem of course is that this would increase the job time, which is no fun when you're standing over the machine, pressing the material down!
I was wondering if several strips of double sided tape (between the workpiece and the sacrificial board) would work? They'd have to be strong enough to hold the material flat (even better if it's strong enough to hold the cut parts, so I don't need tabs) but would have to be easy to remove afterwards (from wood and MDF). I guess it'd also have to not gum up the cutting bit, and be thin enough to not seriously affect depth accuracy. Not asking for much am I?
On a final note, I've been using both up and down cut spiral bits (1/4" diameter). Whilst they cut well, I do get quite a bit of 'fluffy' edging on parts cut from MDF. This is only on the top/bottom surface and is easily removed with a bit of sandpaper, but it is time consuming when you've got lots of parts. Is this just what happens, or is this indicative of rpm/linear speed too slow or fast?
Any thoughts from 'them wot know' greatly appreciated!